/*
   层级大小
   [z-normal]{
       z-index:1;
   }
   [z-top]{
       z-index:1000;
   }
   [z-popper]{
       z-index:2000;
   }
*/
@each $style in (normal $index-normal, top $index-top, popper $index-popper) {
  [z-#{nth($style,1)}] {
    z-index: #{nth($style, 2)};
  }
}
